The explosion of growth in the portable wireless electronics industry has provided numerous challenges and opportunities for manufacturers of radio frequency (RF) components. The latest portable wireless telephony, data, and Internet access products demand greater functionality, higher performance, and lower cost in smaller and lighter formats. Additionally, wireless applications are spreading to new markets—from radar-equipped passenger vehicles to biomedical devices that, when injected or inserted, send data to a receiver outside the body. This demand has been satisfied in part by major advances in integrated circuit (IC) device technology and by the introduction of smaller packaging form factors, smaller discrete passive components, and high-density interconnection printed circuit card technologies.
The RF sections of portable wireless products call for a range of active device technologies combined with high-performance passive components. The ongoing development of active device integration and the trend toward greater functionality have placed great pressure on the need to integrate passive components. Indeed, as many as ninety-five percent of the components in a typical cellular telephone product can be passive components. Consequently, these passive components can occupy a large portion of the circuit board area and commensurately contribute to a large share of product assembly costs. Therefore, integrated passive device technologies hold great potential for significantly reducing circuit board area and product size and weight and/or for allowing increased functionality at a given product size.
Cellular phone radio transmitters use several passive components for functions such as filtering, impedance matching, and switching. For example, a harmonic filter is typically used for signal selectivity over radio bands, while an RF coupler may be used for signal level sensing and control. In conventional applications, a harmonic filter and an RF coupler are two distinct components, each of which adds to the overall device footprint. Recent innovations include the integration of the harmonic filter and the RF coupler on a surface of a semiconductor substrate, referred to as two-dimensional integration. The two-dimensional integration of these components can facilitate reduction of the footprint of the module and simplify fabrication processes relative to the use of two distinct components. In addition, the two-dimensional integration of these components can improve coupling performance, impedance matching, and other operating characteristics. Yet challenges remain in the further reduction of the device footprint and cost while concurrently simplifying fabrication processes and providing effective coupling and directionality.
Microelectromechanical systems (MEMS) components include microfabricated mechanical systems, such as switches, sensors, gyroscopes, and so forth, on a semiconductor chip. In general, MEMS technology is directed to the integration of mechanical elements, sensors, actuators, and electronics on a common substrate through the utilization of microfabrication technology. While associated electronics are fabricated using integrated circuit (IC) process sequences, the micromechanical components are fabricated using compatible micromachining processes that selectively etch away parts of a silicon wafer or add new structural layers (e.g., by deposition), to form the mechanical and electromechanical devices. In this way, MEMS represents a complete system-on-a-chip, free of discrete, macro-scale, moving mechanical parts.
The development of microelectromechanical systems (MEMS) components for wireless applications is growing due to their low cost, small area, and high performance. Indeed, in some applications such as an RF re-configurable system, the integration of MEMS devices with RF components, such as integrated passive devices, offers space and cost savings, higher performance and reliability, smaller form factors, and lower cost as a result of high-volume, high-yield IC-compatible processes relative to the use of discrete components. However, again challenges remain in further reducing the device footprint relative to the footprint achieved utilizing two-dimensional integration of integrated passive devices and MEMS components, reducing cost, and simplifying fabrication processes.